Visual indicating radio direction finder



July 26, 1938- N. COULTER ET AL 2,124,544

YISUAL INDICATING RADIO DIRECTION FINDER Original Filed Oct. 23, 1,935 2 Sheets-Sheet l F1 5 l v Ll, V

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a DETECTOR 3 INVENTORS HOWARD N. COUUER GERHARD R.F|SHER waw ATTORNEY Original Filed Oct. 23, 1935 Local OJc/l/afor AT+ Lp H. N. COULTER Er AL VISUAL .INDICATING RADIO DIRECTION FINDER 2 Sheets-Sheet 2 AMPLIFIER 1 D ETEGTOR -|NVENTOR$ HOWARD N. COULTER GERHARD RAFISHER.

ATTORNEY Patented July 2c, 1938 UNITED STATES "PATENT. OFFICE VISUAL mmcarme namo nmsorrou Howard .N. Collier, United States avy, s... Pedro,andGcrhardB.Fishe:-, ll View,

ApplicationOctober 2:, 1935, Serial m. (6.314

9 Claims. 250-11) (Granted under the act of Bach amended April 30,1928; 370 0- G. 75'!) y i This invention relates to radio direction finding systems, more particularly to such systems whereinreceptionof intelligence is accomplished simultaneously with the determination of the ,5 direction of the transmitting station.

A specific object of this invention is to provide an essentially automatic system for use on navigable craft whereby the navigator is enabled to keep closely to a predetermined course. .It is further possible to ascertain the exact position of a vessel by taking bearings 01 one ormore radio transmitting stations by either rotating a loop antenna or turning ,the vessel or aircraft provided with a fixed directional antenna. 4

When applied to aircraft, the system aids in locating landing fields and is of special utility when the navigator is flying over unfamiliar territory. The invention is manifestly of particular utility under conditions 01' poor visibility.

A further object of this invention is to provide a radio direction finder that requires little or no manipulation by the operator.

A further object of this invention is to provide a radiodirection finder with a visual indicator which permits the taking oi! bearings with more positive accuracy and with more speed,

. than by means of aural methods.

Avstiil further object of the invention is to provide .a system having a directional loop antenna in which by locking the loop in a zero posi-' tion, the instrument can function as a visual homing indicator.

Another object of the invention is to provide a direction finder in which the equipment permits continuous listening-in to the transmitting station even when taking bearings. The ordinary radiodirection finder operates on a minimum or null. signal which usually results in 4 blanking out reception'of telegraph or speech during the actual taking of a hearing.

The equipment requires no sense indicator, nor any procedureior determining the sense of a bearing, other than to note which direction of 4 rotation of the loop is required to move the visual indicator to the right or left. 7

Inadvertent taking of a bearing 180 degrees but will cause no delay norerror, as reverse bearings are always exactly 180 degrees in error. Whereas ordinary direction finder receivers require manipulation 01 a balancing condenser during the taking of bearings, this equipment requires no balancing condenser. This device possesses visual and aural means for indicating perfect balance in the loop circuit at any time,-

toemploytheusuaimeans of balancing heretofore used in radio direction finders.

Thesignalessentiallyusedispickedupby the antenna, and not the loop, the loop Signal 5 merely providing a superimposed signal necessary ior determining direction. For this reason greater distance ranges can be obtainedthan with the ordinary direction finder.

An additional important feature is that due to 10 its inherent modulating system,'either cw or modulated continuous wave signals can be received at all times without any switching or adjustment.

The,device can beutilined by aircraft for the 15 approximate determination of drift .due to wind under conditions when the surface 01 the earth is totally obscured.

This equipment enables the operator to ascertainthepresenceotnight"orsimilarefi'ectboth 20 visuallyandaurally,andfurthertodetermine intermittently during periods when such efiect is generally existent, brief periods when the efi'ect is absent, under which conditions bearingscanbetakenwhichcanbedefinitelyknown 25 tobeireeoi'the abnormalerrorcausedbysuch This direction finder does not makeuse oia um signal but utilizes the full strength oithesignalreceivedfromanopenantennaat 30 all times. Operating on the maximum signal strength obtained from an open antenna'connectedtoaradioreceiverinsuchawayasto obtainradio' it permits the full use ofaflsnalprop rlytnnedtoitsmaximumand 5 thus permits the taking! radio'bearlngs even through'heavy. interference n'om ons oncloselyadjacentirequenciesandthroughlocal man-made interference and'static.

the simultaneous on at one location or radiodh'ectionfinderbearlngstaken bytwoor 45 more distantly located direction finders. Another-object of this invention is to provide ',a direction finding system of the character described in which the number of pieces of appa- 'ratusrequiredand theirweightmaybesmallm so as to reduce the weight required to be car ried byanairplane.

Inthisdirectionfindersystemthemdesirableefiects oitimingordetuningthe open an tennainrelaiiontotheloop antennaareenflre- 55 1y eliminated with the result that diet of the radio frequency circuits will not afiect the radio bearing.

By using a modulated carrier and a special filtered receiver and loop circuit, the direction finder can be kept immune from interference except when such transmission uses exactly the same carrier radio frequency and audio ire- Referring to Fig. 1, 14 represents the loop antenna, A represents an open non-directive antenna. A radio signal from a distant station is received by antenna A and amplified by means of tube Tl. The plate circuit of tube T55 is coupled to the input of radio receiver 2, which consists of several stages of radio frequency amplification, a detector and audio amplifier. The resulting signal is received in the headphones 5. The signal from this open non-directive antenna will never change in strength due to any variation of the directional position of the vessel relative to the transmitter, and regardless of what position the receiver is oriented.

In addition to the above described receiving system, a loop antenna or spaced directional antenna Lp is provided which may be either tuned or untuned, the center of this directional system being grounded at d, and the leads Lot and L122, respectively, being connected to the grid circuits of tubes T8 and T2. The plate circuits of Ti and T2 are connected to coils Li and L2 which in turn are coupled inductively to L3 which rep-- resents the plate circuit of T 3 and tothe input circuit LG of the receiver 2. L9 and L2 are wound in such a way that they oppose each other. In the plate circuit of tubes Ti and T2 is further incorporated a balancing resistance RG and a visual indicator l having a scale marked "Left- Zero-Right. A local audio frequency oscillator is provided consisting of tube T3, and an oscillating transformer M consisting of primary and secondary windings p and 'pi the secondary being center tapped. The outside terminals of pi are connected to the cathodes of tubes Ti and T2, respectively, and the center tap of pi is connected to the secondary of transformer AT and thence to ground. The primary of AT is connected to the output of receiver 2. Current is received by A, amplified by Til, amplified further, detected and amplified at audio fremiency in the receiver 2. The signal'may be observed in the telephone head set 5, on a shadow timing device 7 l, in ,a filtered output meter 3. or by means of a tuned reed indicator 5. Energy is also received by means of the loop or directional antenna Lp having a figure i3 characteristic. This loop antenna may be tuned for reception. Perfect symmetry is obtained by grounding at l the loop 140 in its exact center. The outside terminalsof the loop are connected to the grids of tubes Ti and T2, so that the radio frequency in aiaaeae the loop is amplified and coupled to the receiver 2 in such a way that the radio frequency currents of Li and L2 neutralize each other. The cathode voltage of tubes Ti and T2 is varied by a local A. 0. generator in such a way that while one tube operates on the straight portion of its grid voltage-plate current characteristic curve,vthe other tube operates on the curved portion, with the result that the amplified R. F. current in Ll will add to the currents received by A at one instant, and subtract therefrom at the next instant. This local generator also has a tendency to modulate any CW signal received by the loop. If the loop is in such a position that noradio frequency current will be received by it, the tubes Ti and T2, and coils Li and L2 will not transfer any radio frequency energy to L3 or to Lil. Incorporated in the cathode circuit of tubes Ti and T2 is a transformer AT. .This transformer is connected in such a way that the output voltage is combined with the voltage produced by oscillator T3 and then impressed upon the cathodes of Ti and T2.

The bias of the potential E on the cathodes of Ti and T2 should be selected so that these tubes operate on a curved portion of their grid voltage-plate current characteristic curve, so that during V2 cycle, at frequency V produced by the local oscillator, increased plate current will flow in Ti and very little plate current will flow in tube T2. During the next /2 cycle these conditions will be reversed. RE is balanced in such a way that these changesin plate current will cause main at zero reading.

Now, when radio frequency energy is received by antenna A, (but not by the loop), after being detected and amplified in receiver 2 and the output voltage thereof impressed with the oscillator voltage upon Ti and'T2, no fluctuation of the indicator i results. If, however, the loop antenna is receiving R. F. energy at the same no fluctuation in the indicator 3, and it will rethe loop antenna the phasing between loop and antenna currents can be materially changed, so that with the loop antenna receiving no voltage from the distant transmitter the visual indicator will read zero, and with the loop turned to the right the indicator will move right, and with the loop turned to the left the indicator will move left. In some installations it is necessary to connect a resistor R2 in series with the antenna A to produce the proper phasing. In general, bad distortion effects are ordinarily incurred as a result of combining tuned antennas with loops. By using a buffer stage as shown any undesirable efi'ects are eliminated.

As above set forth, a voltage component derived-from the output of receiver 2 is, through transformer AT, impressed upon the center'tap of secondary pi and thence upon the cathodes of tubes Ti and T2. It is obvious that the component thus impressed upon said cathodes will be at the frequency of the output of receiver 2 and also of oscillator T3, from which it is derived, and that it will have'the same phase oncomponent does not have a constant relation to that ofthe voltage in pl but varies in accordance with the direction of deviationof the plane of loop Lp from perpendicular to the path of the 5 181181 and hence destroys the balance existing be- 5 into-receiver 2.

In Fig. 2 are shown juxtaposed for purpose of comparison. the magnitudes of the various voltages at different points in the circuit during the different cycles of operation. When loop La:

50 is at right angles to the line from the loop to the source In of the received energy, as'in the uppermost portion of the figure, all voltages in the loop are equal and opposite and there is no resultant efi'ect on indicator i. Next below are :5 shown the conditions when Lp is rotated to the right; the voltages from the loop are still equal and opposite, as are those from transformer AT, 1 but the phase relations are such that the resultant of the two gives a small current from T2 and i) a large current from TI, causing indicator l to give an indication righ The lowermost part of the figure depicts L2 turning to the left, with a resultant greater voltage on T2 than on Ti and a greater plate current from T2, producing the indication left; a

As antenna A always receives a maximum sig- 'nal on account of its non-directional characteristics, reception of messages is possible even when taking bearings. v Due to the perfect symmetry employed in the circuit, no balancing condenser is required.

The direction finder can be checked at any time for proper operation by observing that when visual indicator l reads zero, the modulation irequency of the local oscillator should not be heard in the'phones nor be observed in any of the visual indicators shown in Fig. 1. If these two conditions do not check, there. exist two possibilities: (1) a breakdown of electrical circuits in the di 0 rection finder, or (2) the existence of night orsimllarefi'ect. Duringactualtestsitwas observed that during the presence of night effect the indicator could be keptat aero whereas the modulating frequency would actuate any of the indicators shown in the output of receiver 2; or

the efiect of the modulating frequency could be kept out oi the same indicators, but the visual .indicator Ii would continuously swing to the right and left, indicating the presenceof night etiect.

After some time all indicators would again act normally simultaneouslyand so show that the disturbing influences had subsided, thus enabling the taking'of normal bearings.

As antenna 4 represents an essential part for receiving the signal, .it is this antenna which determines the range of the direction finder.

J By taking simultaneous readings on the radio direction finder and magnetic compass and observing any change in the visual indicator-on the calibrated loop'scale, it ispossible to approximately determine and make correction for thedriftoianaircraftdue'tothewind.

local electrical-interference, static and mani made interference will afiect this direction finder to aircraft it is evident that 3 onlysllghtly due to its inherent balancing charac- It is possible to connect as many visual indicators in parallel as necessary to make simultaneous observations at difierent locations, of

bearings being taken.

By means of reslstor Rl it e possible to move the pointer of indicator i from its center position and in such a way apply any corrections which might be desired. Fig. 3 shows variations in the wiring of the direction finder in which it is not necessary to return the output of receiver 2 to Tl, or T2. This is accomplished by using an electrodynamometer.

'This simplifies the circuit as no transfer of the receiver output energy to the loop circuit is required.

In addition to the indicators provided in the output circuit of receiver 2 it is possible to include a neon tube in the same circuit to determine the silent sector above a radio transmitting station.

To permit aircraft to home" despite interfer I once, a variation of the direction finder circuit is shown in Fig. 4. In this system, the local oscillator necessary for modulating the loop circuit is eliminated, and the voltage necessary for this modulation is derived from reception of a modulated continuous wave signal, in which the audio frequency modulation is predetermined, and this received audio frequency energy is passed through a filter circuit in the direction finder. The audio frequency voltage so derived is in turn applied by means of a center-tapped transformer 180 out of phase to the grids of Tl and 132. Thus even if there should be set up radio interference on exactly the same carrier frequency, the aircraft would still be able to "home unless the carrier frequency was continuously modulated withexactly the same audio frequency modulation.

While this invention is especially adaptable it also can be used forpther purposes. 1

It is obvious from the preceding description that this invention is not confined specifically to the circuits asshown, but that different means may be employed for combining the signal energies intercepted by the directive and non-directive absorbing means, or that other changes may be made which do not aifect the underlying principles of this invention.

The invention disclosed herein may be manufactured and used by or for the Government of the United States without the payment of any royalty thereon. I

We claim: 1

1. In a direction finding system, a pair of amplifying-thermionic tubes, a directional loop antenna grounded at its midpoint, connections extending from the terminals of said loop to the d electrodes of said tubes forming input circuits for said tubes, output circuits including a coil for. each of said tubes, said coils being wound in such a way that they oppose each other, means for causing said tubes to alternately operate, one as an eihcient amplifier operatingon the relatively straight portion of its grid voltage plate current characteristic cln've while the other oper ates on the curved portion, a substantially nondirectional antenna, means for amplifying and detecting radio frequency waves, means for im-. pressing on the input circuit of said last means the radio frequency waves amplified by said pair ,of tubes and the radio frequency waves derived rrom said non-directional antenna, means for applying a component of potential between the cathode and the grid electrode of each tube of said pair of tubes in at the output frequency detected by said detector and means connected in the output circuit of said tubes and responsive to the difierence between the value or the -average anode current in said pair of tubes for indicating the relative position of said loop antenna with respect to a radio transmitting station transmitting waves received by said antennae.

2. A direction finding system in accordance with claim 1 in which a visual indicator is connected to beenergized solely by the output currents from said means for detecting radio frequency waves.

3. A" direction rm system in accordance with claim i in which an audible signal indicator is connected to said means for detecting radio frequency waves whereby said system may be used for the reception of intelligence simultaneousiy with its use-as a direction finder.

4. A system in'accordance with cl 1 in which an indicator tor indicating the presence of night effect is connected to be energized by the output from saiddetector.

5. A system in accordance with claim ii in which both visual and aural indicators are con-' nected to be energized by the output from said detector.

6. In a direction finding system, a substanfialiy non-directional means for receiving a radio frequency wave irom a'transmitting station, a second means for receiving a radio frequency wave from the transmitting station, said second means comprising a loop antenna having a grounded midpoint, a pair of thermionic amplifying tubes, meansconnecting one of the terminals of said loop to the control grid of one of said tubes,

tional primary winding to be energized under 7 control of the radio frequency waves received by said non-directional means, an amplifier and detector connected to the secondary winding of greases said transiorm'er for amplifying the algebraic sum or the waves impressed thereon and detecting the same, means for varying the potential difference between the grid electrode and the cathode of each of the tubes of said pair in phase in accordance with the detected component of current derived from said detector, means including a device having a substantially constant low frequency output for causing said tubes to alternate- 1y operate, one as an emcient amplifier operating on the relatively straight portions of its gridvoltage plate current characteristic curve while the other operates on the curved portion, and means for indicating which of said pair of tubes has the greater average output current flowing therein and for indicating the value of the dinerential current. V

7. A system in accordance with claim 6 in which an indicator for indicating the presence of night{ efiect is connectedto be energized bysaid detector. v Y

8. In a. direction finding system, a. pair of heater type thermionic amplifying tubes having cathode, anode and control electrodes, a; directional loop antenna connected to the control electrodes of said tubes so as to impress thereon received radio frequency waves of the same frequency and amplitude but of phase difierence in the two tubes, 9. source of modulating frequency connected to the cathodes of said tubes to vary the potential of said cathodes with respect to ground at the same frequency and amplitude but at 180 phase erence in the two tubes, a substantially nondirectional antenna, means for amplifying and detecting radio frequency waves,- means for simultaneously impressing on the input circuit of said last means the radio frequency waves set up in the output circuits of said pair of tubes and the radio frequency waves from said non-directional antenna, means for varying in phase the potential of both of the cathodes of said pair of tubes with respect to ground at the frequency derived from said detector and an indicating device responsive' to the difierence of current flow in the output circuits of said pair of tubes.

9. A system in accordance with claim 8 in which an indicator for indicating the presence of night efiect is connected to be energized by the means for detecting radio frequency waves.

now u. coumnn. W s i R. FISMR. 

